It is known to use adhesives to prepare artwork for photography or client approval by sticking the various components such as photographs, headlines, etc. into their desired positions on a layout board. The adhesives used in this application should be simple to use allowing the components to be re-positioned as desired but providing sufficient adhesion between the components and the layout board so that the components do not come off during handling. Furthermore, the adhesive should be easily cleaned off the layout board without leaving a stain when a component has been initially deposited in an incorrect position.
Solvent based rubber adhesives have been used for this purpose but they are messy and difficult to spread uniformly over a surface. Water based adhesives are also messy and produce the additional problem of paper curl. Spray adhesives require spray areas and adequate ventilation when being applied. Hot melt and thermal adhesives require special applicators, the applicator for the former being expensive and its use involving a time-delay in which the adhesive is heated up. In the latter case, the artwork components cannot be repositioned.
Transfer adhesives have been proposed which overcome the above problems. In these adhesives, an adhesive coating is applied to a release substrate and then a protective cover sheet is applied to the coating to form a transfer sheet. In use, an area corresponding to the size of the component to be adhered is cut out from the sheet, the cover sheet removed and the adhesive is pressed onto the surface of the component. The substrate is then removed leaving the component with an adhesive layer. However, problems may be encountered if the adhesive is not correctly positioned relative to the component surface and not correctly cut to size. If the adhesive is too small and/or incorrectly positioned, edges or corners may be left with no adhesive and will be prone to lifting.
Alternatively, the cover sheet can be removed, the component placed in contact with the exposed adhesive, and then the component and its adhesive are separated from the remainder of the adhesive sheet by cutting around the edge of the component. This is problematic as the cutting has to be done with the adhesive exposed, which can be messy and the adhesive may not be correctly applied.
One approach to overcome the problems mentioned associated with the use of transfer adhesive sheets is to make the adhesive coating shearable. In such an arrangement, the component is pressed on to the adhesive once the cover sheet has been removed and as the component is pulled away, the adhesive shears to provide the surface of the component with a complete covering of adhesive which extends to the edges of the component. However, the additives which have to be used to make the adhesive shearable, for example, silica, tend to reduce the cohesiveness and tack of the adhesive. This results in the adhesive smearing instead of being removed when the component to which it is adhered is deposited initially in the wrong position and has to be repositioned.
British Patent Specification 1384423 discloses a further approach to overcome the problems mentioned above. In this document, substantially non-contiguous adhesive segments are disclosed which are formed on a release substrate, the adhesivity between each segment and the substrate being less than the adhesivity between the segment and the surface to which it is to be affixed. As each segment is substantially non-contiguous with adjacent segments, a surface pressed on to the adhesive coating will only pick up adhesive on that surface and each segment will be easily separated from any other.
Adhesive transfer sheets according to British Patent Specification 1384423 can be produced by printing. However, in order to form an eventual strong adhesive bond (supplying sufficient adhesive) it is necessary to form a coarse pattern of the adhesive segments. This makes such transfer sheets unsuitable for use in adhering small items, for example a single line of 6 point type being stripped into text. Furthermore, printing processes which are used to produce such transfer sheets are both slow and expensive when compared with web coating processes.